United States: Mosquito-borne illnesses have been gaining attention across the United States. Infections such as West Nile virus, Eastern equine encephalitis (EEE), malaria, and dengue have been spreading in an unseen manner. Experts have suggested that a possible reason behind the spread of infections or diseases is the warming of the world.

While sharing the stats, the local authorities mentioned that New York City has reported as many as 490 cases of West Nile Virus since the turn of the century. It is to be noted that the disease is spread by infected mosquitoes. Notably, one of the cases linked to the disease was Anthony Fauci – the chief medical advisor to the US president from 2021-2022.

Once largely confined to the regions of East Africa and the Middle East, the West Nile virus has stealthily entrenched itself within New York and steadily proliferated across the United States. In 2023, over 1,100 mosquito pools, predominantly in Queens, were identified as carriers of the virus. As of 2024, cases have been confirmed in 39 states. A vast majority of infections estimated between 70-80%, exhibit either mild symptoms or none at all; however, severe cases risk leading to enduring neurological impairments, according to reports by BBC News.

What is more disconcerting is the resurgence of Eastern equine encephalitis (EEE), another mosquito-borne ailment notorious for its lethality, with a staggering 30% fatality rate. First recognized as a public health menace in 1938, sporadic outbreaks have steadily increased, particularly in the northeastern United States over the past two decades. EEE cases are even appearing farther north, marking a concerning trend. Although infections remain uncommon, the 2019 outbreak—boasting a record of 38 cases—stands as a stark reminder of its potential. As of 2024, 10 EEE cases have emerged across six states, prompting aggressive mosquito control measures in Massachusetts to stem further transmission.

Infectious disease authorities caution that such erratic mosquito-borne pathogen behavior is becoming increasingly commonplace. A striking case emerged in New Hampshire, where a man was hospitalized in September 2024 after contracting not one but three mosquito-borne illnesses simultaneously—West Nile fever, EEE, and St. Louis encephalitis.

Biologist Chloé Lahondère of Virginia Tech observes that the phenomenon of multi-pathogen infections is on the rise. Globally, mosquito-borne diseases are surfacing in previously atypical regions. Locally acquired cases of malaria resurfaced in the US in 2023 after a 20-year hiatus. Dengue fever has also made an appearance in California and Arizona, with Europe grappling with record outbreaks and deadly dengue surges striking Peru.

The Climate Nexus

Much of this startling shift can be attributed to evolving climatic conditions. Rising temperatures have enabled mosquito populations, particularly those that serve as vectors for diseases like West Nile and dengue, to invade new territories. For example, species within the Aedes genus, alongside Culex coronator, have successfully established themselves in previously hostile environments. Since its detection in Louisiana in 2004, C. coronator has steadily migrated across southeastern states, bringing diseases such as West Nile and St. Louis encephalitis along for the ride, as reported by BBC.

Sadie Ryan, a professor of medical geography at the University of Florida, notes the surprise at the northward appearance of Aedes-borne diseases like dengue in California. “The mosquito species had been quietly infiltrating traps far north within the state, unnoticed at first, though they’re not yet firmly established. However, it serves as an ominous warning.”

Even remote high-altitude regions are not immune to this encroachment. Once considered malaria-free, the hills and mountains of Nepal now face a rising incidence of the disease. “Malaria was traditionally viewed as a lowland affliction,” says Paul Tambyah, president of the International Society for Infectious Diseases, “but with warming climates, mosquitoes can now survive at previously unattainable altitudes.”

The health implications are profound. Mosquito-borne illnesses already afflict an estimated 700 million people each year, claiming one million lives. Projections suggest that over the next century, an additional billion individuals, primarily in Europe and subtropical regions, will contract these diseases for the first time. Regions like Asia and sub-Saharan Africa, where such infections have been seasonal, may see transmission year-round.

Understanding Mosquitoes’ Biological Response

Mosquitoes, being cold-blooded, are highly sensitive to environmental temperature fluctuations, with every aspect of their short life—bite frequency, maturation rate, and aging—governed by external warmth. For example, Aedes triseriatus can thrive at a relatively cool 22°C (72°F), allowing it to range from Florida to southern Canada. By contrast, Aedes aegypti prefers balmier climates, flourishing at 29°C (84°F). As temperatures rise, the range of these species and their disease transmission capacity broaden.

Ryan and colleagues have discovered that warmer climates are extending mosquito breeding seasons, which directly correlates with the increased prevalence of mosquito-borne diseases. “If temperatures increase within a tolerable range for mosquitoes, species can expand their habitats and reproduce at an accelerated rate, leading to larger populations capable of significantly impacting public health,” noted Lahondère.

Warming Isn’t the Only Factor

One particularly adaptive species, Aedes albopictus, has been a notable beneficiary of our warming world. Thriving at approximately 26°C (79°F), its survival prospects have been bolstered by milder winters and extended spring and autumn periods in North America and Europe. This has allowed A. albopictus to carve out a vast niche, now occupying 36 US states and sprawling across Europe.

Moreover, A. albopictus is adept at hitching rides with human transportation, facilitating its spread into new areas. Erin Mordecai, an infectious disease ecologist at Stanford University, explained, “Unlike A. aegypti, A. albopictus is resilient enough to withstand colder climates, allowing it to colonize the eastern United States. It’s now a serious invasive threat, capable of transmitting dengue, chikungunya, Zika, and other viruses,” as per BBC News.

In addition to warming, climate change has escalated the frequency of both floods and droughts. These extremes provide ample breeding grounds for mosquitoes. A collaborative study between the Technical University of Mombasa and Stanford University found that stagnant floodwaters in small containers offer ideal mosquito breeding conditions. Urbanization and increased human mobility further compound the issue, driving up dengue outbreaks globally.

The Role of Human Activity

Environmental pollution is a lesser-known but significant factor in mosquito proliferation. Certain species, such as Aedes aegypti and Anopheles stephensi (the malaria mosquito), thrive in the discarded plastic waste that often holds stagnant water, creating perfect breeding grounds. A single Aedes mosquito can lay 200 eggs in the cap of a soda bottle, according to Ryan. “Bits of litter with just a small amount of stagnant water can quickly become mosquito nurseries,” she warned.

Beyond discarded plastic, mosquitoes also breed in any human-made container capable of holding water, from old tires to plant saucers, whether in urban backyards or sprawling landfills. Lahondère added that Aedes species are now opportunistically feeding on ornamental plants and wildflowers in urban settings, adapting to exploit available sugar sources.

The Path Forward

While individual actions like removing standing water are important, Lahondère stresses that larger systemic solutions are essential. Political commitment to addressing climate change and investments in public health infrastructure, such as vaccine development and mosquito control initiatives, are urgently needed. Scientists are exploring promising interventions, from deploying toxic sugar baits to genetically sterilizing mosquitoes.

Although these approaches may hold the key to mitigating the scourge of mosquito-borne diseases, Lahondère cautioned, “A mosquito-free future seems unlikely, but a future where their impact is diminished is within our reach.”